Natural rubber industrially used currently is derived from Hevea brasiliensis (Para rubber tree). However, since the region where Hevea brasiliensis can be cultivated is limited, there is a high demand for alternative plants producing natural rubber.
As an alternative plant producing natural rubber, Taraxacum kok-saghyz (Russian dandelion) has been drawing attention because natural rubber can be obtained from its roots, and temperate zones can be selected to cultivate it. Accordingly, methods for extracting rubber from this plant have been under development.
In order to create new varieties of crops suited to specific purposes, crossbreeding techniques are often used. These techniques involve breeding or crossing different varieties with different properties to create new varieties with new properties. For crossing, it is necessary to cause plants to bloom and be pollinated. Thus, the crossbreeding techniques require flower bud formation.
In order for plants to shift to the flower bud formation stage (reproductive phase), factors such as: (1) age of the plants, (2) photocycle, and (3) temperature are known to be important.
For example, with respect to (2) photocycle, plants are roughly divided into long-day plants which start forming flower buds when the sunshine duration increases above a certain length; short-day plants which start forming flower buds when the sunshine duration decreases below a certain length; and neutral plants which form flower buds regardless of the photocycle.
Chrysanthemums, which are short-day plants, are treated as follows. For example, the lighting duration is extended to suppress flower bud formation until they grow large enough to sell as products, but once they are large enough, the lighting duration is shortened to promote flower bud formation (see for example Patent Literature 1).